Field of the Disclosure
Embodiments of the disclosure relate to a touch sensing system and a method for driving the same capable sensing a pen and a finger.
Discussion of the Related Art
A user interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been indispensably used in portable information appliances and has been expanded to the use of home appliances. The touch UI senses a location of a finger or a pen touching a touch screen and generates location information.
The touch screen is classified into a touch screen sensing a conductor, for example, the finger, and a touch screen sensing the pen. An example of the latter pen touch screen is disclosed in U.S. Pat. No. 7,903,085 (Mar. 8, 2011) (hereinafter, referred to as “a related art pen touch sensing device”). The related art pen touch sensing device includes a special pen including a resonant circuit embedded therein, a loop antenna receiving a resonance signal from the special pen, and an analog signal processing unit extracting location information and pen pressure information of the special pen from a signal of the loop antenna.
As shown in FIG. 1, in the related art pen touch sensing device, a square wave signal for inducing a resonance circuit of a pen PEN is propagated through an electromagnetic resonance path, i.e., the electromagnetic field, to an antenna ANT and is transmitted to the pen PEN. A resonance signal generated from a resonant circuit of the pen PEN is propagated through the electromagnetic resonance path and is received by the antenna ANT. The resonant circuit of the pen PEN is resonated by the square wave signal received through an electromagnetic resonance, i.e., the electromagnetic field and transmits the resonance signal to the loop antenna in the electromagnetic field. Thus, in the related art pen touch sensing device, the pen PEN and the antenna ANT transmit and receive the resonance signal in the electromagnetic field.
The related art pen touch sensing device inputs the resonance signal received through the loop antenna to an analog circuit. The analog circuit includes a location decision circuit deciding a location of the pen based on a phase of the resonance signal received through the loop antenna and a pen pressure decision circuit deciding a pen pressure of the pen based on the phase of the resonance signal.
The related art pen touch sensing device, however, has the following disadvantages.
The related art pen touch sensing device requires the plurality of loop antennas and switch circuits for sequentially driving the loop antennas, so as to detect a touch location of the pen in an XY coordinate system. The loop antennas have to be implemented in an overlapped shape in a matrix form, so as to recognize a touch point in the XY coordinate system. Further, because a separate antenna layer has to be added to a display panel so as to implement the loop antennas in the display panel, the thickness of the display panel increases. Because a structure for connecting the plurality of loop antennas and the analog signal processing unit to the display panel has to be added, a cable connection equipment becomes large and complicated. Thus, when the plurality of loop antennas are integrated in the display panel, it is difficult to provide a slim and simple display device.
Because the related art pen touch sensing device compares received signals of the pen using an analog comparator, only the presence or absence of the pen may be recognized and it is difficult to accurately represent coordinates of the touch location of the pen.
Because the related art pen touch sensing device additionally includes the location decision circuit and the pen pressure decision circuit, the circuit complexity increases and also an amount of operations increases. Hence, power consumption increases.
Because the phase of the resonance signal in the related art pen touch sensing device sensitively varies depending on a surrounding environment, it is difficult to accurately detect the phase of the resonance signal due to parasitic capacitances of the loop antenna.
The related art pen touch sensing device calculates an arctangent value of the resonance signal and measures the pen pressure. As shown in FIG. 2 showing an arctangent characteristic curve, a nonlinear period is formed at “−pi” and “+pi”. This is because the arctangent value is initialized every 2π (360°). Because of this, change in the arctangent value depending on a phase difference of the resonance signal is discontinued at predetermined time intervals. Thus, the related art pen touch sensing device has to set a range of a resonant frequency except the nonlinear period.
Because a pulse generator used in the related art pen touch sensing device limits a frequency region of the resonance signal, it is difficult to change the resonant frequency.
Because the analog signal processing unit used in the related art pen touch sensing device shows different operation results depending on the surrounding environment, such as a temperature and humidity, its reliability is low.